// let arr1=[1,2,3],arr2=[1,2,3];
// let arr3=arr1;
// arr3[1]='a'
// console.log(arr1,arr3);
// let arr4=arr1.concat();
// arr4[1]='b';
// console.log(arr1,arr4);
// let arr5=[...arr1];
// arr5[1]='c';
// console.log(arr1,arr5);



// let arr = [[1, 2, 3], [10, 11, 12], 100, 200];
// let copyArr = arr.concat();
// // copyArr[2]=1000;
// copyArr[1][1] = 'abc';
// console.log(copyArr);
// console.log(arr);



// let a = 10, b = 15;
// [a, b] = [b, a]

// let arr6 = [1, 2, 3]
// let [z, x, c] = [1, 2, 3]

// let [user] = [['zhangsan', 123, 500]]

// let arr = [100, 200, 300];
// arr.push(500);
// console.log(arr.length);